Manufacturers of vehicles that employ internal combustion engines, more particularly diesel engines, are under increased pressure to comply with current and future emission standards for the release of oxides of nitrogen (NOX), particularly nitrogen monoxide (NO), as well as unburned and partially oxidized hydrocarbons (HC), carbon monoxide (CO), particulate matter, and other emissions, such as hydrogen sulfide (H2S) and ammonia (NH3). In order to reduce the previously mentioned emissions of a diesel engine, the latter are typically operated with exhaust gas after-treatment systems through which the exhaust gas from the diesel engine flows.
Exhaust gas after-treatment systems typically include one or more after-treatment devices, such as oxidation catalysts, NOX abatement devices, diesel particulate filters (DPFs) and sulfur traps. These after-treatment devices generally require certain conditions to exist in the engine exhaust gas in order to perform optimally. More specifically, NOX abatement devices and oxidation catalysts, for example, have a relatively narrow temperature window within which the devices are activated, regenerated, or operate with high conversion efficiency. Periodically, after-treatment devices require heating beyond that provided by the exhaust gas to achieve the desired operating temperature, such as in the case of DPFs.
Additionally, DPFs periodically require a relatively high concentration of oxygen in the exhaust gas to facilitate regeneration of the particulate filter. Often, the required exhaust gas conditions cannot always be achieved during normal operation of the engine. More particularly, the exhaust gas temperature can only be influenced to a certain degree by the combustion process without the use of a source of supplemental heat, such as an electric heater in the exhaust-gas stream. The particulate matter can generally be characterized as soot that is captured and reduced by DPF. Present DPFs contain a separation medium with tiny pores that capture particles. Resistance to exhaust flow in the DPF increases as trapped material accumulates in the DPF, thereby generating an increase in exhaust backpressure. The DPF must then be regenerated to burn off the particulate matter/soot in the particulate trap to reduce the exhaust backpressure and increase exhaust flow through the DPF. A typical method of regenerating a DPF utilizes an energy source such as a burner or electric heater to encourage combustion of the particulate matter. Particulate combustion in a DPF has been found to increase the exhaust gas temperature within the vehicles exhaust system, downstream from the DPF.